This research involves the design and testing of reversible inhibitors which may be analogous in structure to activated intermediates in enzyme catalysis. These compounds may be of medicinal use as antimetabolites. The enzymes under investigation include deaminases for cytidine and adenosine, glycosidases, L-asparaginase, carbohydrate isomerases, an proteolytic enzymes of various kinds. Based on mechanistic information available about these enzymes, a guess is made about the probable structure of active intermediates, and compounds with similar binding properties are synthesized and tested for inhibitory potency. In successful cases, chemical reasoning and exact structural methods are used in an effort to determine interactions at the active site, in order to obtain mechanistic information and to make further improvements in inhibitor design.